Here's the short list of reasons I don't like him:
1) He voted for the Iraq war
2) He is buddy buddy with Jerry Falwell, the guy who said Americans deserved 9/11 for sinning
3) He hopes to appoint SCOTUS justices who will overturn Roe vs. Wade
4) After originally opposing the Bush tax cuts on the wealthy, he did an about face and started sucking the party cock so he could get support for the nomination. (I personally am only concerned about the 'death tax')
5) He's softened his stance/rhetoric against torture based on party pressure
Just because he's a war hero doesn't make him unequivocally principled. The man is a schmuck.
Frankly what I don't like about him (or any of the front runners) is that I can't name a single significant difference between any of them. During the next presidency, I predict we'll see:
1) Ongoing Iraq war with little to no meaningful end (causing #2)
2) Massive inflation. I'm praying we don't hit double digits.
3) Skyrocketing food and other commodities prices based on a shitty dollar(resulting from #2)
4) Skyrocketing healthcare costs (admittedly the candidates will accomplish this goal differently)
5) Stagnant wages for most workers
6) Either a continuation of or an enhancement of domestic spying
Frankly, I don't see any appreciable difference between any of the remaining candidates with respect to what I foresee happening during the next 5 years.